The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The construction of automotive bodies and other manufactured products may utilize several uniformly sized electrical resistance spot welds. The welding is performed using a weld gun typically having copper or copper alloy welding electrodes. The sheet metal between the electrodes is briefly melted during current flow and then re-solidifies to form an integral weld nugget of suitable diameter at the abutting surfaces of the sheet metal layers. In manufacturing operations, hundreds of these spot welds are rapidly formed.
Generally, in such operations the welds are substantially the same size, within an acceptable tolerance value, and/or with minimal internal porosity or discontinuities. However, undesired variations can occur in the welds because of electrode wear. The electrode tip may become misshapen to have a mushroom-like shape that must eventually be repaired or dressed, either by hand or by machine, to remove the misshapen region. After a number of dressings the electrodes may become shortened in length and require replacement. Also, as the electrodes are progressively worn, the surface area of the tip of the electrode may increase, and accordingly the current density may decrease. This decrease in current density is known to affect the quality of the spot weld.